1. Field of the Invention
This invention relates to the dyeing of cotton, flax, hemp, wool, silk, and blends of such materials with synthetic materials, in the form of yarn, fabric, or woven or knitted articles of clothing, in a batch or continuous process.
2. Summary of the Background Art
Vat dyes form a large class of dyes that are applied to textile fibers in chemically reduced leuco forms that are water soluble. Then, an oxidation process is applied to return the leuco forms to insoluble dyes having the desired colors on the surfaces of the fibers or dispersed through the fibers, depending on the materials and process. This large class of dyes can be used to produce a wide variety of colors in textiles.
The most widely used vat dye is Indigo, which has been used to dye cellulose-based textiles, such as cotton, for centuries. Since indigo is practically insoluble in water, ether, alcohol, and dilute acids, conventional dyeing processes include reducing the indigo dye to a soluble leuco form having a yellow-green color, using a suitable reducing agent with an alkaline material. After the fabric material is then exposed to the leuco form in a bath, the fabric material is exposed to air or oxygen so that the reduced dye within the fabric is oxidized, returning to an insoluble form in which the blue color is apparent. Since, even in the leuco form, indigo has a low affinity for textile materials, these steps are repeated as often as needed to obtain the desired shade of blue, with five to seven immersions typically being used, and with each of these immersions being followed by an oxidation process.
Conventional processes for dyeing fabric materials with sulfur dyes also include a step of chemically reducing the dye before it is applied to the material. For example, after being made water soluble by chemical reduction, a sulfur dye is applied within a pad-steam process to be subsequently squeezed off under a defined pressure. Then, the dye is diffused into the fibers during a steaming process. Alternately, in a pad-dry-pad-steam process, the sulfur dye is applied to the fabric in a dispersed or dissolved form and is then squeezed off under a defined pressure. Then, a downstream chemical pad is applied, impregnating the fabric so that dye diffusion into the fibers is achieved by steaming. Either of these processes is followed by rinsing and oxidation of the dye, resulting in through dyeing of the fiber.
In a pad-dry process, a reduced sulfur dye is applied to the fabric to be subsequently squeezed off under a determined pressure. The treated fabric then passes through a pre-dryer having a downstream hot flue, in which the dye material is partially oxidized, and through additional rinsing and oxidation. While the dye material remains at the surface of the fiber, its level of fixation is undesirably low, leading to difficulties in establishing a consistent and reproducible dyeing process.
For both fabric materials dyed with vat dyes, such as indigo, and for fabric materials dyed with sulfur dyes, a significant market exists for materials dyed with a controllable and reliable “surface dyeing” process, in which a layer of dye material is adhered to the surface of the yarn or fabric without substantial penetration within the substrate. Such materials can be mechanically abraded to produced a “stone-washed” appearance, with a portion of the dye material being removed from the surface to reveal an undyed or differently colored core within the fiber. Alternately, such material may be chemically treated, for example with enzymes, to change the color of a part of the outer surface so that a similar appearance is produced.
Commercially successful processes for dyeing cotton fabrics with indigo have been generally limited to continuous processes for dyeing warp yarn to be used in the production of blue jeans and other denim products. Such a continuous process is described, for example, in U.S. Pat. No. 3,457,022 as a process in which the yarn is first dipped in hot dye solutions to achieve maximum penetration of the dye within the yarn, which is then repeatedly dipped in cold dye solutions to obtain the desired color.
Other patents describe the chemical components of the dye bath. For example, U.S. Pat. No. 4,166,717 describes a process in which the indigo is reduced to its soluble leuco form with sodium hydrosulfate and maintained in an aqueous solution with sodium hydroxide. An aldehyde addition product, such as formaldehyde, acetaldehyde, or furfural, is added to the solution, with an adduct, such as a bisulfate or a sulfoxylate.
U.S. Pat. No. 5,935,273 describes a process for the continuous dyeing of yarn containing cellulose in a single passage through an aqueous solution of indigo in its reduced, or leuco, state in a dye liquor additionally containing deoxidants, alkali, and a dissolved alkali metal salt at a concentration of 100 to 200 grams/liter as an electrolyte as a pH value of the liquor is adjusted to about 10.2 to 11.3. As the electrolyte concentration is maintained, the yarn is exposed to a gas that dissolves in the aqueous solution while forming an acid. Suitable gasses are carbon dioxide, hydrogen chloride, formic acid vapor, and acetic acid, with carbon dioxide being preferred, with the use of carbon dioxide to establish maintain and control pH in dyeing processes being further discussed in U.S. Pat. No. 5,295,998, and with the use of carbon dioxide to effect an accelerated neutralization of cellulose textile substrates being additionally discussed in U.S. Pat. No. 4,536,907. Then the reduced indigo in the yarn is oxidized to form a pigment, with the dyeing process.
The conventional process includes labor-intensive steps associated with the handling of the yarn, such as warp beam make-up and yarn quilling. To eliminate such steps, what is needed is a method for dyeing garments instead of the yarn used in their production. Additionally, dying garments provides for effective inventory control, and for the color coordination of garments containing different types of yarns or knitted and woven materials.
U.S. Pat. No. 4,845,789 describes a process for the rapid dyeing of a series of successive garments or batches of garments with a vat dye, preferably indigo dye. While the garments are being constrained, they are submerged in, and impregnated with, a dyeing solution in a first bath. Then, they are removed from the first bath and held with the draining from them to be conserved for reuse. Next, the garments are promptly immersed in an oxidizing solution in a second bath to shock oxidize the dye present in the garments, which are then removed from the oxidizing bath while draining the oxidizing solution and preserving it for reuse. The garments are then washed and dried. The time between removal of the garments from the dyeing solution and their placement in the oxidizing solution is less than five minutes.
U.S. Pat. No. 4,756,037 describes a process for dyeing with a vat dye, such as an indigo dye solution, a series of successive garments made with fabric containing cellulose. The garments are supported on supports that keep all fabric surfaces of each garment accessible to treating solutions, so that the materials are uniformly impregnated with a dye solution at a first bath. The garments are then inserted in an oxidizing solution within a second bath to uniformly oxidize the dye present within each garment.
U.S. Pat. App. Pub. No. 2005/0097685 A1 describes a process for producing a reproducible ring dye using sulfur dyes on fabrics containing textile fibers and on blended fabrics containing textile fibers. The process comprises, following the application of a sulfur dye vat to the fabric, a step in which the dye is fixed and incipiently oxidized at a temperature of 80 to 160 degrees C., and preferably between 120 and 130 degrees C., and at a moisture content of 5 to 50 percent, and preferably between 20 and 30 percent.
U.S. Pat. No. 4,131,423 describes a process for dyeing fibers using a water-insoluble dye, such as a sulfur dye. The process comprises reductive dissolution and oxidative fixing using an oxyhalogen acid as an oxidizing agent.
U.S. Pat. No. 4,322,214 describes a process for dyeing textile materials, such as fiber and cloth more satisfactorily with sulfur dyes or sulfurized vat dyes, with an organic mercapto compound and/or an organic sulfur compound capable of generating mercapto groups under dyeing conditions being present in dye baths. Still more improved dyeing results may be obtained by allowing a sulfite salt compound to be further present in such dye baths.
The patent art additionally describes a number of other methods for treating textile material and blends including cellulose to improve dyeability. For example, a method for producing anionically dyeable smooth dry crosslinked cellulose is described in U.S. Pat. No. 5,298,584, with a cellulose-containing material being modified with a combination of a hydroxyalkylamine or a hydroxyalkyl quaternary ammonium salt, one or more glycols, and a crosslinking agent. The reaction is typically catalyzed with salts such as zinc nitrate or magnesium chloride, used either alone or in conjunction with citric acid. Types of usable anionic dyes include acid, direct, and reactive dyes. The cellulose-containing material may be in the form of fibers, yarns, slivers, and paper. U.S. Pat. No. 5,139,530 describes the production of anionically dyeable smooth-dry crosslinked textile materials by treatment of methylolamide crosslinked textile materials with an alkali swelling agent such as sodium hydroxide before dyeing. U.S. Pat. No. 3,576,589 describes a method for dyeing a fabric, such as a polyester/cotton fiber, in a vat/disperse dye system, using hydroxylamine sulfate under conditions of thermal fixation. The hydroxylamine sulfate is maintained at a pH in the range 5.0 to 6.5 in a vat/disperse dye pad to obtain maximum penetration of the dye within the fibers of the fabric. U.S. Pat. No. 4,767,421 describes a method of manufacturing a homogeneous water-insoluble dye layer on a substrate, with a solution of a cationic or anionic dye in an organic solvent being provided on the substrate, with the solvent being removed, and with the resulting dye layer being treated with am aqueous solution of a salt. The cation of the anionic dye is exchanged for the cation of the salt. Alternately, during treatment with an aqueous solution of a salt or acid, the anion of the cationic dye is exchanged for the salt or acid.
U.S. Pat. No. 5,647,875 describes a method for producing a desired color shade by treating a dyed textile substrate, which has an initial color shade, partly due to color caused by the presence thereon of a vat dye and partly due to color caused by the presence thereon of a sulfur dye, with a chlorine-free decolorizing agent, such as hydrogen peroxide, in an aqueous alkaline medium. The color shade is modified by removing a portion of the color attributable to the sulfur dye within removing as large a proportion of the color attributable to the vat dye.
What is needed is a method for dyeing fabrics and garments formed from fibers including cellulosics, wool, and silk with a vat dye, such as indigo, as well as for dyeing the yarn used to make such fabrics and garments. Additionally, what is needed is a method for dyeing cellulosics, wool, and silk without relying on multiple dips to get a suitable shade. Furthermore, what is needed is a method allowing the use of batch processes, such as pad-jig dyeing and dyeing within a rotary dyeing machine to dye textile materials with indigo. Additionally, what is needed is a controllable method for reliably and consistently ring dyeing various substrates with vat and sulfur dyes, so that a satisfactory level of adhesion of the dye is consistently achieved at the surface of the fibers.